These investigations extend ongoing studies of LH and FSH clearance kinetics aimed at analyzing both quantitative and qualitative aspects of changes in LH and FSH secretion. This information will be applied to studies of GnRH-stimulated LH and FSH synthesis and release not only in vitro but in vivo. Some of the in vivo studies will utilize a phenobarbital-treated rat in which endogenous "GnRH" secretion appears to be minimally effective or abolished. Efforts will be made to characterize pituitary secretory responses in terms of their component processes (synthesis, release, and any intermediate processes such as storage, or shifts between "releasable and "non-releasable" pools). This information will be applied in the study of steroid modulations of GnRH effects, using a variety of steroid treatments, principally with dihydrotestosterone (a "pure" androgen), in order to characterize both the possible extents of these actions and to elucidate possible mechanisms of both GnRH and steroid actions. Additional experiments will be done in intact rats to compare overall effects on LH and FSH secretion of steroid treatments which stimulate or exceed the normal feedback signals from the gonad. Comparisons of these findings with information about the response capabilities of the "isolated" pituitary will form a basis for inferences about steroid (and other) effects on "GnRH" release. In all three types of preparations, responses to GnRH will be used to examine both long-term and short-term effects of castration and steroid treatment, in order to define the evolution of the castration response and of its prevention or reversal by steroid treatment.